Abstract

Microcavities for organic light-emitting devices (OLED’s) with a metal mirror on one side and a distributed Bragg reflector (DBR) on the other side have been extensively studied in the literature. Usually the DBR is highly reflective, and the resulting emission of the microcavity depends strongly on angle and wavelength. With a thick metal mirror on one side and a semi-transparent metal mirror on the other side of the OLED, a microcavity can be obtained with an optical thickness of 1 half-wavelength. Because the emission is enhanced over a wide solid angle, with a small spectral dependence, this structure is very promising for display applications. For a TPD/ALq3 structure with a typical intrinsic emission spectrum, embedded in a microcavity with a thick and a semitransparent silver mirror, the integrated emission in air, the color variation with angle, and the change in the decay time are compared with those in a DBR-based microcavity.

Figures (5)

Structure of the Alq3–TPD-based OLED for the silver/silver microcavity (left) and the silver/DBR microcavity (right). The light is generated in the 10-nm-thick Alq3 emitting layer, near the Alq3–TPD interface. Above the emitting layer there is a nonemitting Alq3 layer with variable thickness. Below the emitting layer there is a TPD layer and an ITO layer. Because the refractive indices of these materials are nearly the same, the thickness of the ITO is included in the effective TPD layer thickness. The definition of the directions + and - are indicated by the arrows with those labels. The distances indicated on the right illustrate the nonemitting Alq3 thickness; the effective TPD thickness; the total distance between the mirrors, de; and the distance between the light emitting region and the upper mirror, z-.

Simulated relative power distribution Prel(αglass,λ) as a function of the angle in glass and the wavelength, assuming a flat intrinsic spectrum. Top, for the silver/silver structure (7); bottom, for the silver/DBR structure (8).

Top, polar plot of the simulated emission in air, integrated over the Alq3 spectrum given in Fig. 2, for the silver/silver structure (7) and the silver/DBR structure (8) compared with the reference case (REF) without reflections. Bottom, simulated variation of the x CIE chromaticity color coordinate with the angle of emission in air for the two structures, based on the Alq3 spectrum.